Client/server computing has become more and more important over the past few years in the information technology world. This type of distributed computing allows one process (a "client") running on a machine to delegate some of its work to another process (a "server") running on another machine that might be, for example, better suited to perform that work. The client and server might also be two processes running on the same physical machine.
The benefits of client/server computing have been even further enhanced by the use of a well-known computer programming technology called object-oriented programming (QOP), which allows the client and server to be located on different (heterogeneous) "platforms". A platform is a combination of the specific hardware/software/operating system/communication protocol which a machine uses to do its work. OOP allows the client application program and server application program to operate on their own platforms without worrying how the client application's work requests will be communicated and accepted by the server application. Likewise, the server application does not have to worry about how the OOP system will receive, translate and send the server application's processing results back to the requesting client application.
Details of how OOP techniques have been integrated with heterogeneous client/server systems are explained in U.S. Pat. No. 5,440,744 and European Patent Published Application No. EP 0 677,943 A2. These latter two publications are hereby incorporated by reference. However, an example, of the basic architecture will be given below for contextual understanding of the invention's environment. In this example, the client and server are on different machines, but, the same software architecture applies if they are on the same machine.
As shown in FIG. 1, the client computer 10 (which could, for example, be a personal computer having the IBM OS/2 operating system installed thereon) has an application program 40 running on its operating system ("IBM" and "OS/2" are trademarks of the International Business Machines Corporation). The application program 40 will periodically require work to be performed on the server computer 20 and/or data to be returned from the server 20 for subsequent use by the application program 40. The server computer 20 can be, for example, a high-powered mainframe computer running on IBM's MVS operating system. For the purposes of the present invention it is irrelevant whether the requests for communications services to be carried out by the server are instigated by user interaction with the first application program 40, or whether the application program 40 operates independently of user interaction and makes the requests automatically during the running of the program.
When the client computer 10 wishes to make a request for the server computer 20's services, the first application program 40 informs the first logic means 50 of the service required. It may for example do this by sending the first logic means the name of a remote procedure along with a list of input and output parameters. The first logic means 50 then handles the task of finding and establishing the necessary communications with the second computer 20 with reference to definitions of the available communications services stored in the storage device 60. All the possible services are defined as a cohesive framework of object classes 70. During this process, the first logic means 50 determines an object reference which has one component (the server address) identifying the server computer 20 and another component (the object key) identifying the particular server object located on server computer 20. Defining the services in this way gives rise to a great number of advantages in terms of performance and reusability.
To establish the necessary communication with the server 20, the first logic means 50 determines which 50 object class in the framework needs to be used, and then creates an instance of that object, a message being sent to that object so as to cause that object to invoke one of its methods. This gives rise to the establishment of the connection with the server computer 20 via the connection means 80, and the subsequent sending of a request to the second logic means 90.
The second logic means 90 then passes the request on to the second application program 100 (hereafter called the service application) running on the server computer 20 so that the service application 100 can perform the specific task required by that request, such as running a data retrieval procedure. Once this task has been completed the service application may need to send results back to the first computer 10. The server application 100 interacts with the second logic means 90 during the performance of the requested tasks and when results are to be sent back to the first computer 10. The second logic means 90 establishes instances of objects, and invokes appropriate methods of those objects, as and when required by the server application 100, the object instances being created from the cohesive framework of object classes stored in the storage device 110.
Using the above technique, the client application program 40 is not exposed to the communications architecture. Further the service application 100 is invoked through the standard mechanism for its environment; it does not know that it is being invoked remotely.
The Object Management Group (OMG) is an international consortium of organizations involved in various aspects of client/server computing on heterogeneous platforms as is shown in FIG. 1. The OMG has set forth published standards by which clients (e.g. 10) communicate (in OOP form) with servers (e.g. 20). As part of these standards, an Object Request Broker has been defined (known as the Common Object Request Broker Architecture, or CORBA for short), which provides the object-oriented bridge between the client and the server. The ORB decouples the client and server applications from the object oriented implementation details, performing at least part of the work of the first and second logic means 50 and 90 as well as the connection means 80.
Oftentimes, duplication of server resources (in the form of plural servers) is provided to enable "the server" to handle a large number of simultaneous client requests and to provide for fault tolerance (if one server is defective another can "step in" and take over). The clients think they are communicating with a single "server", but in fact, a plurality of servers are actually handling the requests (these servers could be located on separate machines, or they could be separate processes running on the same machine). In this context, client requests destined for "the server" are directed to a central gateway (common to all of the server machines making up "the server") which performs workload management and load balancing to distribute client requests to the various servers according to any well-known workload balancing policy (or combination of a plurality thereof), such as the round robin by method policy, where each server is assigned a request in turn. The specific details of the balancing policy/policies to be used are selected by the person configuring "the server" system architecture, typically a systems administrator.
A major problem with this type of approach is that all client request traffic on its way to "the server" must first pass through the gateway, which is, in essence, a bottleneck. Thus, if client request traffic destined for "the server" increases, it may take a considerable amount of time for a request to make its way through the gateway and into one of the plurality of servers located behind the gateway. The clients are thus made to wait to get an answer from a server for a period of time that may be unacceptable, especially as the number of clients that may wish to gain access to a server continues to increase.
A second problem is that should the gateway fail for some reason, no client requests will be serviced. In other words, the gateway is a single point of failure which, if it fails, will prevent the rest of the system from continuing operation.